I just wonder that makes you so excited．
A.why it doesB.what he doesC.how it isD.what it is在线课程D
解析：
考查宾语从句，此题的宾语从句为强调句型，后应用陈述句语序，句意：我只是想知道究竟是什么使你如此兴奋。所以选D。